From 3390f50dcf1834674a9c0c8ec9851027026bb6d8 Mon Sep 17 00:00:00 2001
From: "Alexander J. Pfleger" <70842573+AJPfleger@users.noreply.github.com>
Date: Thu, 5 Dec 2024 16:02:19 +0100
Subject: [PATCH] feat: safe inverse for dynamic matrices (#3945)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

- **New Features**
	- Enhanced the `safeInverse` function to support dynamic matrices in addition to fixed-size matrices.

- **Tests**
	- Added a new test case for the `safeInverse` function to validate its behavior with dynamically sized identity matrices.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->
---
 Core/include/Acts/Utilities/AlgebraHelpers.hpp   |  5 ++---
 .../Core/Utilities/AlgebraHelpersTests.cpp       | 16 +++++++++-------
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/Core/include/Acts/Utilities/AlgebraHelpers.hpp b/Core/include/Acts/Utilities/AlgebraHelpers.hpp
index 06379ec3559..aa522a7dbc2 100644
--- a/Core/include/Acts/Utilities/AlgebraHelpers.hpp
+++ b/Core/include/Acts/Utilities/AlgebraHelpers.hpp
@@ -178,7 +178,7 @@ inline ActsMatrix<A::RowsAtCompileTime, B::ColsAtCompileTime> blockedMult(
 /// Calculate the inverse of an Eigen matrix after checking if it can be
 /// numerically inverted. This allows to catch potential FPEs before they occur.
 /// For matrices up to 4x4, the inverse is computed directly. For larger
-/// matrices, the FullPivLU is used.
+/// matrices, and dynamic matrices the FullPivLU is used.
 ///
 /// @tparam Derived Eigen derived concrete type
 /// @tparam Result Eigen result type defaulted to input type
@@ -192,12 +192,11 @@ std::optional<ResultType> safeInverse(const MatrixType& m) noexcept {
   constexpr int cols = MatrixType::ColsAtCompileTime;
 
   static_assert(rows == cols);
-  static_assert(rows != -1);
 
   ResultType result;
   bool invertible = false;
 
-  if constexpr (rows > 4) {
+  if constexpr (rows > 4 || rows == -1) {
     Eigen::FullPivLU<MatrixType> mFullPivLU(m);
     if (mFullPivLU.isInvertible()) {
       invertible = true;
diff --git a/Tests/UnitTests/Core/Utilities/AlgebraHelpersTests.cpp b/Tests/UnitTests/Core/Utilities/AlgebraHelpersTests.cpp
index 86165ddb2ba..87e47d3e3a9 100644
--- a/Tests/UnitTests/Core/Utilities/AlgebraHelpersTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/AlgebraHelpersTests.cpp
@@ -51,6 +51,15 @@ BOOST_AUTO_TEST_CASE(safeInverseLargeMatrix) {
   BOOST_CHECK_EQUAL(*identityInv, identity);
 }
 
+BOOST_AUTO_TEST_CASE(safeInverseDynamicMatrix) {
+  Eigen::MatrixXd identity{Eigen::MatrixXd::Identity(2, 2)};
+
+  auto identityInv = Acts::safeInverse(identity);
+
+  BOOST_CHECK(identityInv);
+  BOOST_CHECK_EQUAL(*identityInv, identity);
+}
+
 BOOST_AUTO_TEST_CASE(SafeInverseBadSmallMatrix) {
   Eigen::Matrix<double, 2, 2> m;
   m << 1, 1, 2, 2;
@@ -111,13 +120,6 @@ BOOST_AUTO_TEST_CASE(SafeInverseFPELargeMatrix) {
 //   auto mInv = Acts::safeInverse(m);
 // }
 
-/// This test should not compile
-// BOOST_AUTO_TEST_CASE(SafeInverseDynamicMatrix) {
-//   Eigen::MatrixXd m{Eigen::MatrixXd::Identity(2, 2)};
-//
-//   auto mInv = Acts::safeInverse(m);
-// }
-
 BOOST_AUTO_TEST_SUITE_END()
 
 BOOST_AUTO_TEST_SUITE(SafeExp)